How do I modify variables in a fitting model?

I am using the constrained non-linear curve fit VI to fit a non-linear curve and I am using it in the mode where you supply the reference to the VI to do the fitting model. (The dark teal wire wired to the fitting vi)


In my fitting parameters I have n1 and d (refractive index and thickness), however, I also have parameters that I'd like to change on my front panel such as wavelength (lambda) and refractive index n0 and n2 of the surrounding media. I was just inserting these values as constants before (setting as 1.519, etc.) but now I have the need to change them without having to rewrite the reference to the VI every time. How do I do this?